Gearing up for Gravitational Waves: the Status of Building LIGO

1. Gearing up for Gravitational Waves: the Status of Building LIGO Frederick J. Raab, LIGO Hanford Observatory

2. LIGO’s Mission is to Open a New Portal on the Universe • In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy • The boost from “naked-eye” astronomy revolutionized humanity’s view of the cosmos • Ever since, astronomers have “looked” into space to uncover the natural history of our universe • LIGO’s quest is to create a radically new way to perceive the universe, by directly sensing the vibrations of space itself Raab: Gearing up for Gravitational Waves

3. LIGO Will Reveal the “Sound Track” for the Universe • LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for for cosmic cataclysms, like: • Supernovae • Inspiral and mergers of black holes & neutron stars • Starquakes and wobbles of neutron stars and black holes • The Big Bang • The unknown Raab: Gearing up for Gravitational Waves

4. The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) LIGO (Louisiana) Brought to you by the National Science Foundation; operated by Caltech and MIT; the research focus for about 350 LIGO Science Collaboration members worldwide. Raab: Gearing up for Gravitational Waves

5. LIGO Observatories Raab: Gearing up for Gravitational Waves

6. 2-km & 4-km laser interferometers @ Hanford Single 4-km laser interferometer @ Livingston Configuration of LIGO Observatories Raab: Gearing up for Gravitational Waves

7. Part of Future International Detector Network Simultaneously detect signal (within msec) Virgo GEO LIGO TAMA detection confidence locate the sources decompose the polarization of gravitational waves AIGO Raab: Gearing up for Gravitational Waves

8. What Are Some Questions LIGO Will Try to Answer? • What is the universe like now and what is its future? • How do massive stars die and what happens to the stellar corpses? • How do black holes and neutron stars evolve over time? • What can colliding black holes and neutrons stars tell us about space, time and the nuclear equation of state • What was the universe like in the earliest moments of the big bang? • What surprises have we yet to discover about our universe? Raab: Gearing up for Gravitational Waves

9. A Slight Problem Regardless of what you see on Star Trek, the vacuum of interstellar space does not transmit conventional sound waves effectively. Luckily General Relativity provides a work-around! Raab: Gearing up for Gravitational Waves

10. How Can We Listen to the “Sounds” of Space? • A breakthrough in 20th century science was realizing that space and time are not just abstract concepts • In 19th century, space devoid of matter was the “vacuum”; viewed as nothingness • In 20th century, space devoid of matter was found to exhibit physical properties • Quantum electrodynamics – space can be polarized like a dielectric • General relativity – space can be deformed like the surface of a drum • General relativity allows waves of rippling space that can substitute for sound if we know how to listen! Raab: Gearing up for Gravitational Waves

11. “The most incomprehensible thing about the universe is that it is comprehensible” - Albert Einstein General Relativity: The Modern Theory of Gravity (for now) Raab: Gearing up for Gravitational Waves

12. The Essential Idea of General Relativity • Galileo and Newton showed that all matter falls the same way under the influence of gravity; radically different from behavior of other forces • Einstein solved the puzzle: gravity is not a force, but a property of space & time • Spacetime = 3 spatial dimensions + time • Perception of space or time is relative • Objects follow the shortest path through this spacetime; path is the same for all objects • Concentrations of mass or energy distort (warp) spacetime Raab: Gearing up for Gravitational Waves

13. John Wheeler’s Summary of General Relativity Theory Raab: Gearing up for Gravitational Waves

14. Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy Rendering of space stirred by two orbiting black holes: Gravitational Waves Raab: Gearing up for Gravitational Waves

15. In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves. Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work. Energy Loss Caused By Gravitational Radiation Confirmed Raab: Gearing up for Gravitational Waves

16. What Phenomena Do We Expect to Study With LIGO?

17. The Nature of Gravitational Collapse and Its Outcomes "Since I first embarked on my study of general relativity, gravitational collapse has been for me the most compelling implication of the theory - indeed the most compelling idea in all of physics . . . It teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as 'sacred,' as immutable, are anything but.” – John A. Wheeler in Geons, Black Holes and Quantum Foam Raab: Gearing up for Gravitational Waves

18. Do Supernovae Produce Gravitational Waves? Puppis A • Not if stellar core collapses symmetrically (like spiraling football) • Strong waves if end-over-end rotation in collapse • Increasing evidence for non-symmetry from speeding neutron stars • Gravitational wave amplitudes uncertain by factors of 1,000’s Credits: Steve Snowden (supernova remnant); Christopher Becker, Robert Petre and Frank Winkler (Neutron Star Image). Raab: Gearing up for Gravitational Waves

19. Catching WavesFrom Black Holes Sketches courtesy of Kip Thorne Raab: Gearing up for Gravitational Waves

20. Sounds of Compact Star Inspirals Neutron-star binary inspiral: Black-hole binary inspiral: Raab: Gearing up for Gravitational Waves

21. Searching for Echoesfrom Very Early Universe Sketch courtesy of Kip Thorne Raab: Gearing up for Gravitational Waves

22. How does LIGO detect spacetime vibrations? Answer: Very carefully

23. Important Signature of Gravitational Waves Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction. Raab: Gearing up for Gravitational Waves

24. End Mirror End Mirror Beam Splitter Laser Screen Sketch of a Michelson Interferometer Viewing Raab: Gearing up for Gravitational Waves

25. Fabry-Perot-Michelson with Power Recycling 4 km or Optical Cavity 2-1/2 miles Beam Splitter Recycling Mirror Photodetector Laser Raab: Gearing up for Gravitational Waves

26. Spacetime is Stiff! Raab: Gearing up for Gravitational Waves

27. What Limits Sensitivityof Initial LIGO Interferometers? • Seismic noise & vibration limit at lowest frequencies • Atomic vibrations (Thermal Noise) inside components limit at mid frequencies • Quantum nature of light (Shot Noise) limits at high frequencies • Myriad details of the lasers, electronics, etc., can make problems above these levels Sensitive region Raab: Gearing up for Gravitational Waves

28. Hanford and Livingston Lab facilities completed 1997-8 16 km beam tube with 1.2-m diameter Beam-tube foundations in plane ~ 1 cm Turbo roughing with ion pumps for steady state Observatory Facilities Mostly Completed • Large experimental halls compatible with Class-3000 environment; portable enclosures around open chambers compatible with Class-100 • Some support buildings/laboratories under construction Raab: Gearing up for Gravitational Waves

29. Beam Tube Bakeout • Method: Insulate tube and drive ~2000 amps from end to end Raab: Gearing up for Gravitational Waves

30. Beam Tube Bakeout Raab: Gearing up for Gravitational Waves

31. Beam Tube Bakeout Results Raab: Gearing up for Gravitational Waves

32. LIGO I has evolved from design principles successfully demonstrated in 40-m & phase noise interferometer test beds Design effort sought to optimize reliability (up time) and data accessibility Facilities and vacuum system designs sought to enable an environment suitable for the most aggressive detector specifications imaginable in future. Currently Installing LIGO I Detector Raab: Gearing up for Gravitational Waves

33. Vacuum Chambers Provide Quiet Homes for Mirrors View inside Corner Station Standing at vertex beam splitter Raab: Gearing up for Gravitational Waves

34. HAM Chamber Seismic Isolation Raab: Gearing up for Gravitational Waves

35. HAM Seismic Isolation Installation Raab: Gearing up for Gravitational Waves

36. HAM Seismic Isolation Measured in Air at LHO Seismic Design Model Transfer Function Measurements Raab: Gearing up for Gravitational Waves

37. BSC Chamber Seismic Isolation Raab: Gearing up for Gravitational Waves

38. BSC Seismic Isolation Installation Raab: Gearing up for Gravitational Waves

39. Deliver pre-stabilized laser light to the long mode cleaner Frequency fluctuations In-band power fluctuations Power fluctuations at 25 MHz Provide actuator inputs for further stabilization Wideband Tidal IO Role of thePre-stabilized Laser System Tidal Wideband 4 km 15m 10-Watt Laser Interferometer PSL Raab: Gearing up for Gravitational Waves

40. Prestabilized Laser Optical Layout Raab: Gearing up for Gravitational Waves

41. Washington 2k PSL Raab: Gearing up for Gravitational Waves

42. Frequency Servo Performance N. Mavalvala P. Fritschel Raab: Gearing up for Gravitational Waves

43. Suspended Mirrors initial alignment test mass is balanced on 1/100th inch diameter wire to 1/100th degree of arc Raab: Gearing up for Gravitational Waves

44. ITMx Internal Mode Ringdowns 9.675 kHz; Q ~ 6e+5 14.3737 kHz; Q = 1.2e+7 Raab: Gearing up for Gravitational Waves

45. Alignment of 2-km arms worked for both arms! The beam at 2-km was impressively quiet Stable locking was achieved for both arms by feeding back to arms Measured optical parameters of cavities Characterized suspensions Characterized Pre-Stabilized Laser & Input Optics Single-Arm Tests Swinging through 2-km arm fringes Raab: Gearing up for Gravitational Waves

46. Interferometer Control System • Multiple Input / Multiple Output • Three tightly coupled cavities • Ill-conditioned (off-diagonal) plant matrix • Highly nonlinear response over most of phase space • Transition to stable, linear regime takes plant through singularity • Requires adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition • But it works! Raab: Gearing up for Gravitational Waves

47. Digital Interferometer Sensing & Control System Raab: Gearing up for Gravitational Waves

48. Digital Phase Control Test on Phase Noise Interferometer Raab: Gearing up for Gravitational Waves

49. Composite Video Steps to Locking an Interferometer Y Arm Laser X Arm signal Raab: Gearing up for Gravitational Waves

50. Watching the Interferometer Lock Y Arm Laser X Arm signal Raab: Gearing up for Gravitational Waves